The present inventors proposed a method for measuring a voidage of a dispersoid particle using a volume susceptibility (magnetic susceptibility per unit volume) of the dispersoid particle (Patent Literature 1). The present inventors also proposed a method for measuring a surface area of a dispersoid particle, the number of pores formed in the dispersoid particle, and respective average values of diameters, depths, and volumes of the pores using a volume susceptibility of the dispersoid particle (Patent Literature 2).